This invention relates to an apparatus for controlling a continuously variable transmission for use with an automotive vehicle to change the transmission speed ratio in a plurality of steps.
For example, Japanese Patent Kokai No. 60 -26847 discloses an apparatus for controlling a continuously variable transmission operable at a speed ratio changed in a plurality of steps. The transmission control apparatus operates in an automatic mode to drive the transmission at a target or desired speed ratio i* calculated in terms of vehicle speed and throttle position (or accelerator position) and also in a manual mode to drive the transmission at a speed ratio determined in response to a driver's demand. If the driver continues to depress the accelerator pedal with the transmission speed ratio determined in the manual mode, however, the engine speed would exceed an acceptable range and provide a sense of incompatibility to the driver. In order to eliminate such an undesirable tendency, the transmission control apparatus is arranged to perform an automatic correction of the transmission speed ratio to another speed ratio so as to decrease the engine speed. This is effective to perform continuous transmission speed ratio changes without a sense of incompatibility to the driver. It is now assumed that a transmission speed ratio i(1) (first speed) is selected in the manual mode. When the engine speed increases above the acceptable range, the automatic correction is performed to change the transmission speed ratio i(n) from the current speed ratio i(1) to another speed ratio so as to permit a vehicle speed increase while keeping the engine speed at or below the acceptable value. If the automatic correction produces an upshift to the speed ratio i(3), however, the driver's operation of the shift lever to produce an upshift from the current speed ratio i(1) to the smaller speed ratio i(2) (second speed) one step higher than the current speed ratio i(l) will be ignored. As a result, a sense of incompatibility will be provided to the driver.